Oxygen – we all need it, we can't live without it. It's integral to life on this planet. And it's probable that, as you watch this film, you will be breathing in an oxygen atom that was also breathed by Genghis Khan – or by the first ever apes to stand upright on the plains of Africa.

The oxygen that we breathe is made from two oxygen atoms joined together – O2. They were first joined more than 3 billion years ago by the earliest blue-green algae to evolve. The oxygen molecule first came from bacteria and was present in the fires that destroyed the dinosaurs and the chemical reactions in all human cells, and as ozone they protect the earth from radiation. Since then, both together and apart, they've had the most extraordinary adventures. Each of the two atoms in an oxygen molecule is virtually indestructible – so they have been first-hand players in some of the most dramatic events in the whole of Earth's history.It's often said that we are breathing the same oxygen that the cavemen did. The life of a single molecule of oxygen is traced on it's astonishing journey spanning millions of years, from its creation, into photosynthesis, through the age of the dinosaurs, early man, and on into today.